In order to carry out complex machining operations, until now it has been necessary to use one or even several grinding and polishing machines having a plurality of accurately operating tools. Besides single-spindle machines, machines are also known which use a number of machining spindles and also tool changers which can be used to automatically change the machining tools.
In one such known machine (DE 100 29 967 A1) for machining optical workpieces, the workpiece spindles are arranged in a yoke while two tool spindles are arranged according to the so-called gantry concept in a portal structure above the yoke with three linear axes which can be displaced perpendicular to one another. In order to pivot the yoke, use is made here of a torque motor which makes it possible to achieve angle settings with high precision. However, the high engineering complexity required for this prevents cost-effective manufacture of this machine. Furthermore, the use of a tool changer requires mechanical interfaces between the tools and the tool spindles, and therefore the tool spindles require complex integrated clamping systems. However, with these interfaces, it is difficult to achieve the reproducibility required in highly precise grinding machining with regard to the concentricity and planarity of the tool in view of the desired accuracies of around one micrometer.
Combination tools are also known (DE 197 37 217 A1), in which two cup-grinding tools are arranged such that they can be displaced coaxially and axially with respect to one another in order to produce polishable lenses by means of coarse and fine grinding. However, the tool diameter here is limited and both the rigidity of the connection to the spindle and the concentricity of the grinding lips are capable of being improved. The axial displacement of the tools with respect to one another is also susceptible to problems due to the coolant becoming loaded with glass dust.
In a further known method using an associated device (DE 197 51 750 A1), three or more grinding spindles and optionally measurement stations are arranged parallel to one another and next to one another on a common carriage. The number of spindles, the complexity of the spindle control system, the initial outlay, the subsequent adjustments and the increased space requirement of the structure lead to considerable overall costs.
A known type of grinding and polishing machine has been developed by Loh Optikmaschinen AG, Wetzlar, under the name “Toromatic-2 SL”. This machine, which operates according to a “swing spindle” concept, comprises a tool spindle with a respective cutting and grinding tool flanged to the ends of the spindle. In order to be able to bring the respective tool into engagement with the workpiece, the spindle can be pivoted like the head of a revolver about its pivot axis arranged at right angles to the spindle, and can be fixed in these locking positions assigned to the two tools. In order to adjust the angle of the tool spindle with respect to the workpiece spindle, on this machine an additional device is provided which consists of a pivoting head which can be rotated about a further axis and is provided with an additional hydraulic drive. Arranged on the pivoting head, at a distance from the axis of rotation thereof, is the pivot axis of the spindle housing which holds the tool spindle. This arrangement thus requires two different drives for the 180° pivoting of the tool spindle on the one hand and for the angle positioning of the tool spindle with respect to the workpiece spindle on the other hand.
What is needed is a compact and highly accurate grinding and polishing machine which makes it possible in a simple and cost-effective manner to use a plurality of grinding and polishing tools.